We propose to measure the frequency dependence of respiratory impedance by forced oscillations in dogs and man, and the transmural pressure-area characteristics of the larger airways in dogs. Normal, physiologically altered, and abnormal subjects, and excised dog lungs will be studied. Data will be processed using nonlinear regression analysis to compute values for anatomically meaningful parameters in respiratory models containing elements for airway compliance, central and peripheral resistance, and parallel parenchymal resistances and compliances. Parameter values from the two experimental methods will be correlated and compared with more standard parameters. The ultimate goal is to develop a rapid, simple-to-use, sensitive, non-invasive method for detecting and characterizing small changes in pulmonary mechanical functions during the early asymptomatic state of obstructive lung disease and to explore the role of airways compressibility in causing expiratory flow limitation.